This invention relates to an alloy for use in building up industrial components subjected to service conditions requiring good impact toughness, resistance to tempering, and resistance to temper embrittlement. One such application of particular interest is for use in building up and reconditioning steel mill caster rolls.
Steel mill caster rolls typically have a forged or cast core substrate, a build-up layer (also referred to as simply a build up), and an overlayer of stainless steel overlay. It is critical that the build up layer have high yield strength so that the caster roll has sufficient compressive strength that it does not deform in service. It is also critical that the build up layer have high impact toughness so that cracks which tend to form in the overlayer do not propagate into and through the build up layer, that is, to help ensure that surface cracks in the overlay remain in the overlay. Two alloys which are commonly used as build up are as follows:
______________________________________ Alloy 1 Alloy 2 ______________________________________ C 0.13 0.08 Mn 1.0 1.0 Si 0.5 0.5 Cr 2.0 1.5 Ni -- 1.0 Mo 0.5 0.4 v -- 0.15 Fe Bal. Bal. (all % by weight) ______________________________________
These prior alloys are susceptible to temper embrittlement, have low toughness, and are sensitive to cooling rate. Temper embrittlement, in particular, is a loss in toughness due to reheating of a metal deposit, corresponding to reduced Charpy V notch values, and is primarily attributable to carbide precipitation and increase in hardness. As such, these prior alloys can only be deposited employing a narrow cooling rate range in order to achieve the required properties, as cooling rate affects carbide precipitation. It is therefore necessary to interrupt deposition as the welding deposition interpass temperature (IPT) gets sufficiently high as to result in a cooling rate which is sufficiently low to promote carbide precipitation. Having to repeatedly interrupt the deposition of build up significantly reduces productivity. The susceptibility of these alloys to temper embrittlement and sensitivity to cooling rate also has a tendency to reduce the quality and consistency in the build up.